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A perfect mirror means, that all the photons which collided with the mirror will be reflected in the same amount, with the same energy and with the same - except sign - angle. Will the mirror get an impulse from the photons?

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  • $\begingroup$ There are many similar questions with photons and mirror... it would be great if the Title specifically referred to whether mirror gets an impulse $\endgroup$
    – blanci
    Mar 16 at 21:20
  • $\begingroup$ @blanci PSE is a really well designed software and it allows you to edit questions. $\endgroup$ Mar 16 at 21:30
  • $\begingroup$ @ HolgerFielder thanks. I’m worried whether reference links to this question would get messed if we change title? $\endgroup$
    – blanci
    Mar 16 at 21:46
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Yes it will.

Assuming the light is incedent normally the change in the photon momentum is $2h\nu/c$, and consequently the momentum of the mirror will change by the same amount.

If the mirror is free to move it will be accelerated by the light and as a result the light will be slightly red shifted. There is more discussion of this in Can relativistic momentum (photons) be used as propulsion for 'free' after the initial generation? though the question is not an exact duplicate.

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  • $\begingroup$ Nice. Thanks. And the amount of red shift is dependend of the mirrors mass. Then less mass then more shift. $\endgroup$ May 30 '14 at 9:02
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@HolgerFieldler @John Rennie ....Just for good measure and interest I would like to proffer a Maxwellian interpretation of mirrors. A practical mirror, say, aluminum or silver, will feel the repulsive force of Lenz's law. A simple explanation follows: The magnetic component of the impinging plane wave accelerates electron's in the silver, the subsequent magnetic field vector is parallel to the incident magnetic vector, and as we all know like poles repel, vectors in this case. This is Lenz's law. The impedance of free space is 377 Ohms the impedance of the silver will be in the order of Ohms, such a mismatch generates maximum reflection and repulsion, a blackened surface will represent a higher impedance and less reflection, therefore less repulsion. It is interesting to contemplate whether a 377 Ohm piece of "space paper" (often used by microwave engineer's) would reduce the repulsion to zero? No reflection. The E vector attraction cancels the B vector repulsion? Further contemplation suggests for high impedance surfaces (say, above 377 Ohm's, a dielectric material) attraction may occur?

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  • $\begingroup$ @John Rennie ...I know I'm not very popular here in the Physics area of SE, so I'm attempting to change my "TONE", but still using "mainstream EM theory" which has paid my mortgage and kept me in sustenance for over 50 years. I'm trying to avoid history and opinion referring to my own peer reviewed papers. I'm trying but, it is rather frustrating. $\endgroup$
    – barry
    May 21 at 3:52

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